Reciprocating pump



Feb. 23, 1954 s, PRESENTEY 2,669,937

RECIPROCATING PUMP Filed NOV. 8, 1950 FIGS 3 Sheets-Sheet 2 FIG? 44Patented Feb. 23, 1954 UNITED STATES PATENT? 15 Claims. .1

This invention relates to reciprocating pumps of the type comprisingianenclosure .or chamber communicating through intake valves. with e source'of iiuid under an initial pressure, 'and through :delivery valves 'witha space constituting a -rrcever for ia uidunder a fina-l pressure, thesaid v'chamber including va movable wall to which a reciprocating:movement is imparted, thereby inaeh successiue operating cycle, toexpand said capacity and thus to .nil it vthrough said .intake valves,and then to contract said capacity and tizms to levacuate it throughsaid delivery valves, The :above-mentioned movable wall and wili intheensuing disclosure, bedescribed as a-piston: it may indeed be formed asa pist-on lslidable in a cylindrical enclosure-or compression chamber.,but fit might .ius-t :aswell consist of .a :deformable wall element.,such asa bellows, etc.

One object of .my invention is to provide a pump of this kind in theform' of :a mrtalele,

inexpensive and mechanically simple adapted to serve., e. g. as an aircompressor for medical uses, spray, aerosol treatments, tirexinfla-ting,refrigerators andthe like.

Another object is the provision of ra means for f controlling. thereciprocating movements of the movable wall of a pump capacity adaptedto improve the operating conditions of said pump and specifically toincrease `the frequency of 'operation thereof greatly in excess of therange heretol.

fore attainable in apparatus'of the type specitied.

.Various 'devices'.have ybeen suggested in this held, :some of themusing Iconventional mechanical drive transmissions such ascrank-and-con- A.

necting rod systems, while others employ turbines. However, the presenceof rotary parts, bearings, pivotal connections, and so forth, makes suchsystems comparatively expensive and requires a certain .amount of`maintenance ,and lubrication on the part of the user. Another type ofpump is known, the .so-called vibrator pump, wherein a movable wall ofthe intake and compression capacity is coupled with the movable armatureIof an electro-magnet the 4elec- .trical supply .of which is controlledin known manner by the movements of the said armature itself. This typevof apparatus necessarily has a low operating frequency owing to themechanical Aand electro-,magnetical inertia of its compoments and ishardly suitable to the construction of pumps for gaseous fluids, .eventhough it has been used with Esoine .measure of success in connectionAwith .liquid pumps (e. g. :gasoline pumps) My present inventionprovides, ina first aspect,

a drive device for pumps of the type described, wherein thereciprocating movements of the movable Wall of the capacity are producedby an electro-dynamic motor of the type including ia movable windingthrough .the airgap .of a magnetic circuit, said movable wall beingrigidly `coupled with .said movable winding. Owing to this arrangement,it ybecomes possible to eliminate idelicate mechanical members such asshafts, journals, bea-rings, and the like, as well :as lubrication. Theresulting unit is exceedingly rugged, v ery .simple to use., requiringno maintenance 4by tue user and, addition, opens up a whole range ofpossibilitiesof fundamental importance in the field under consideration.

a The apparatus .may be supplied either directly iroin a source ofsubstantially sinusoidal alterhating current "of .suitable frequency,-or through the medium of a device .for `distorting the actuatingcurrent wave form in a way Vto improve the efficiency -of the pump.

More specifically, the invention is directed to a :control or drivesystem characterized by the fact thatthe .force applied to .the movablewall of the. chamber will tbe a succession of pulses spaced byidleintervals. y An analytical investigation into the Aoperation of pumpsprovided with automatic intake and discharge valves, that is valves'adapted to open and close under the 'sole action of the 'pressuredifferentials established between the operating capacity on the one handand the sourceand receiver-spaces on the other., and with due allowancefor the inertia and spring-return characteristics of said valves, showsthat, as a result of my method, it .becomes ,possible to increase to amarked extent the operating frequency (i. e. the number of :operatingcycles per unit time) of a pump without impairing its efficiency: now ahigh operating frequency means a smaller chamber for a given dischargecapacity and hence a smaller, lighter and cheaper pump unit.

'In particular, it becomes possible to select an operat'ing'frequencyequivalent -lto the normal ireuuency of the power-supply or linenetwork, i. e. 50 cycles per second in most cases in Europe, and 60cycles per second in the United StatesJ and this considerably simpliesthe problem of energy .supply to the apparatus of the invention.

The characteristic features and advantages of the invention., as well as.further objects thereof, will appear from the ensuing description,which relates to one exemplary embodiment selected by way ofillustration with reference to the accompanying drawings, wherein:

Fig. 1 is a diagram of a pump of conventional type;

Fig. 2 is a graph of the piston motion in such a pump;

Fig. 3 is a similar graph explanatory of the method of the invention;

Fig. 4 is a partly diagrammatic axial cross section of an air-pumpaccording to the invention;

Fig. 5 is a detail View of a portion of the pump shown in Fig. 4 in adifferent position;

Fig. 6 is an enlarged sectional elevation of the upper part or valve-boxof the pump shown in Fig. 4 showing the structure of some parts 1ndetail;

Fig. 7 is a corresponding View in plan.

Figs. 8d, 9a, and 10a are respectively diagrammatic illustrations ofdifferent electrical circuits which may be used with the apparatus ofthe invention.

Figs. 8b, 9b, and 10b are respectively illustrations of the wave formsproduced by the circuits of Figs. 8a, 9a, and 10a.

As shown diagrammatically in Fig. l, a conventional lift-and-force pumpcomprises a chamber or pump housing i communicating through one or moreinlet or intake valves 2 with a fluidsupply space and through one ormore outlet or discharge valves 3 with a receiver-space, and comprises apiston 4 driven in reciprocation to either side of a reference level A-Afrom a ro'- tary drive shaft 5 through a mechanical movement-convertingsystem 6 of the connecting rod and crankshaft type.

In all usual cases, the Variations of the distance :c of the piston fromits reference level as a function of time are substantially sinusoidalin character as illustrated in Fig. 2. In this graph it is assumed thatat an initial instant, the piston stood at its uppermost position at thestart of its downward or suction stroke, the discharge valve being openor closed, and that the intake valve or valves were closed. After thepiston has started on its downward or suction stroke, the dischargevalve closes under the action of the pressure prevailing in the receiverspace, and possibly under the additional action of a return spring. Adepression is thus generated in the chamber as the piston during itssuction stroke moves away from said uppermost position. As the pistonreaches a certain level :r1 at the time t1, this suction becomes highenough to cause the intake valve to open. At this point the useful partof the intake stroke sets in, and this useful part will terminate as thepiston reaches its lower dead centre position, i. e. the level x2, atthe'time t2. The piston then starts on its compression stroke.. Theintake valve is closed under the action of the internal pressure whichbuilds up, and possibly under the additional action of a return spring,while the discharge valve opens as soon as the piston reaches Aa certainlevel ma at the time t3. At this point the useful part of thecompression and delivery stroke commences.

It is clear that the efficiency of the pump depends essentially on thefraction of the cycle which is occupied by the idle periods required toreach the positions x1 and fc3, that is, to cause the operation of thevalves especially that of the intake valve. The inertia of the valvesbeing imposed by practical considerations, their open- .ing and closurewill occur at a predetermined value of the internal depression, and thefraction of the cycle required to attain this depression will besubstantially constant all other factors being equal, so that if theoperating frequency is increased, in the sinusoidal type of operationassumed, then the remaining part of the cycles duration will, from agiven instant, become insuicient to allow of the chamber beingadequately filled. This will explain the fact that the efficiency of apump operating in the sinusoidal mode of operation, rapidly drops off asthe operating frequency reaches and exceeds a definite value.

In practice, a rate of 900 to 1000 cycles per second is an upper limitwhich is not easily surpassed with the currently known systems.

The chart of Fig. 3 illustrates a method of control or drive accordingto the invention, characterized by the :fact that the displacementsimposed on the piston, instead of being purely sinusoidal in character,rather assume the character of distorted sinusoids or even that ofseparate pulses with intervening idle periods of substantial durationoccurring at the lowermost position of the piston. In particular, duringthe pistons travel from its upper to its lower position, i. e. duringthe suction stroke, the piston is notably accelerated. For a given valueof the inertia of the intake valve or valves, and in order to reach asimilar rate of internal depression as in the corresponding sinusoidalmode of operation, the time ti required by said intake valves to open,is found in such conditions to be reduced as the downward movement ofthe piston is effected faster. The piston remains at its lowermostposition until the time tz and it may be seen that the time availablefor the lling of the cylinder under the action of the pressure in thefluid-source space is correspondingly increased. The instant at whichthe intake valves close and also that at which the discharge valvesopen, is for example t'e., and the remainder of the upward stroke of thepiston is that corresponding to the compression and discharge phase.This upward part of the pulses may have a slope not necessarilyidentical with that of the downgoing part.

It is interesting to consider in reference to Figures 2 and 3 a waveshape factor s, which will be defined as follows:

for sinusoidal operation (Fig. l):

s=(zli) /fi for pulse operation (Fig. 2):

s'=(l'2t'1)/t'i Obviously s' s. Due to the pulse type of opera.- tion,the filling period of the chamber is increased over that obtained in thesinusoidal mode of operation, for an equal frequency: in other words',it is possible to obtain a filling period of such a long duration as mayonly be realized at a substantially lower frequency in sinusoidaloperation; or again, for a given efficiency, it becomes possible toincrease theI operating frequency and hence reduce the volume of thepump. The provision of such a drive using mechanical means becomesimpracticable for comparatively high frequencies. On the other hand, itis exceedingly simple to provide a drive device according to theinvention, which will now be described in detail with reference to theexemplary embodiment of Figs. 4 to 7.

This example relates t0 an air pump consisting of a head plate Illforming the top or valve-box, of frustoconical sectional configuration,of the variable-volume capacity or compression cham'- ber I l, andhaving associated with a flexible wall element or diaphragm of rubber orequivalent exible material Ill (termed hereinafter the reciprocableiluid displacement member) `which provides lower wall. This diaphragmmay consist of a disc simply `cut out ci a sheet Aof rubber, or aspecially formed part, e. g. a molded cap as illustrated. The diaphragmis clamped aft its periphery between the vmargin or rthe head plate iland 'an-letal annulus lf3 which in turn is rigidly7 mountedin ya generalcylindrical casing M. The compression chamber i yi communicates throughaelmmnferential set of apertures l5 vsealed by 'an armular'f-intakc valvei 6 with'the atmosphere, and through a central passage H sealed byadischarge valve 18, with a receiver space not shown. The details ofthis` section of the pump are Avisible in Fig. '7, where it `is seenthat the intake valve i6 isapp'lled against the orifices It by a springi3 in the form -of va spider wedged at its corners in-a circular groove2l) formed. for this pur-pose in the upper part of chamber il. Theintake 'valve is preferably y-inovided with splines such as yIlia at itsunder face, .and 'projections such as 19a formed on :the spring 'I9 (e.g. simply punched or struck out therefrom) engaging into a groove denedby these splines. As a result of this device, a kind of self-centringeffect is obtained for the intake valverineinber, which averts thenecessity of'having to mount "this member in a guide `conduit andthereby reducing the pressure losses at intake. Itis further lsee-n that'the ydischarge valve member 118 consists of a spider-shaped lia-ngeapplied over the discharge passage by a spring-21| abutted against a nut22 lscrewed in a cylindrical boss or socket 23 lserving `as a union forconnecting the pump `with any load apparatus.

The central part vof the movable wall element il! .(Fig. 4) is clampedbetween a thin rigid disc 23 and a cap 24 formed with a frustoconicalflange 25, the prei-'lle of this cap member conforming substantially tothat of the upper part of cham "y:

ber Il. The cam 2'4 is secured to the top of a cylinder 26 made ofplastic material or light nonmagnetic alloy, longitudinally slotted and-providing a bobbin or casing for a winding 2l arranged in the airgap ofa magnetic circuit '218 including a Acore '29 and a eld plate 3D; the`magnetic field in sa-idcircuit may be permanent or it may be providedby an exciter winding such as 3|. It will be recognized that anelectro-dynamicv motor is-'thus provided of the kind used `for instance'in loud-speakers, and which inthe present instance will 'be adapted toimpart a reciproca-tory motion to the movable wall element I2 ofthe pumpupon a suitable alternating current being made to flow through themovable winding '27.

. The movable winding is suspended from and centred by two spidermembers 32, 33 outwardly clamped lbetween clamping rings 34, 35 and vtheanni-1111s I3, and inwardly between circular rings 36, 31 provided forthis purpose `on the free outer surface of the cylinder 26. Thesespiders may each 'be widely recessed in the way well known in the art oflloud-speaker construction, and they may be made from plastics orresilient metal or any other suitable material. When made of resilientmaterial, they may participate in assuring the resilient return actionrequired inthe motion assumed by the movable coil.

Several sets of holes 38, 39, 4b, 4l place the casing in communicationwith the atmosphere and prevent the occur-rence of any excess pressureoutside the compression chamber of the pump itself. Similar aperturesv42 may :be formed in the movable cylinder 2i as well.

'Tl-ie motor as a whole is secured in the `Icasing 6 ill, for instance'by la nut 43, while the valve-box is. secured by bol-ts 44. The motorthus provided may be supplied sinusoidal alternating current, ibutpreferably, -ac- -cording tothe invention andas stated previously,

a supply of the pulse type is used, whereby all of the -diilcultiesencountered in apparatus `of conventional and purely mechanical design,Aare averted. vIn either case, the movable Winding v.in the movable walll2 of 'the compression chamber `Ill v1will move between a lowerm'ostposition, shown in Fig. '4, and an uppermost position, which may be thatillustrated in Fig, i5. It is interesting .to note that, owing to theelectrodynamic drive of the invention, it becomes quite practicable andsafe 'to increase the amplitude of the movements of the `movable wall'element to a point where said Wall `element will strike the ceiling `ofthe .compress-ion chamber, that is, the amplitude of the drive currentmay ce chosen Iequal or greater than the value for which the stroke of.the movable wallfelement becomes equal to the height .dimension vof thechamber.; for the drive is so :fisicible as to preclude any possibility4of breakage.

The frusto-conicalilange 25 of the cap 24 provides a :support for thefree portion of .the exible wall .element i2 and Asupports the sameduring the period yor compression when the Wall element basa tendency tobe inflated. Owing to this ar rangement, the flexible wall element iis'practically subjected to no resilient .stress whatever, its 'operationbeing restricted to .a sequence vof Sto-andfro buckling movement-s toeither :side of its clamped margin.

.A very important advantage of the device 'according to the inventionlies in the possibility ci operating it at the frequency of the network,i. e. at either 50 cycles or 60 cycles per second A(3006 or 3600 perminute), as the case maybe. greatly simpliiies the problem .ci supply.the-simplest wayfof providing a pulse-drive device according 'to theinvention, is to supply it with simply recticd A.C., as is showndiagrammaticallyin Fig. Sa., Fig. 8b showing the wave form produced bythe larrangement of Fig. 8a, 0f course, any of a wide number of knownmeans, may be used to foreshorten the duration of the pulses applied;thus, polarized rectifiers (Fig. 10c), .shunted rectiilers (Fig. 9a),grid-control thyratrons, saturated transformers and inductors, etc.,`may be used. Figs. 9b and '10b respectively show the wave formsproduced by the circuits ci Figs. 9u and 10a.

Experience shows that with the use of simply rectied A.C., hence with aiilling period, i. e. an idle .inter-pulse period, hardly if at alllonger vin duration than one half-cycle, very satisfactory efficiencyfactors are already obtained at a rate of 3000 or 3600 cycles perminute, as supplied 'by the usual networks.

.It appears hardly necessary to lay stress on the advantages provided bythe invention; still, vI may again emphasize the ease with which pulsesof 'known and predetermined wave form maybe provided, the elimina-tionof all delicate mechanical organs (shafts, bearings, reciprocating rods,and the like? and of lubrication, etc.

The 'invention is by no means restricted :to the single form ofembodiment illustrated and described by way of example. Numerous and-diverse developments and/or variants may obviously be conceived. Thus,the invention is applicable to a pump using a piston or a diaphragm. Inthe case of an apparatus of the type described, practicallynoiselessoperation may becbtainedby 'lining the valve members and theupper face of the disc 23 with a thin coating of rubber or equivalentsubstance.

What I claim is:

1. A fluid pump device comprising a casing, a head-plate, a recess insaid plate, a flexible diaphragm, means for peripherally clamping saiddiaphragm around said recess, said recess and said diaphragm dening avariable volume chamber, intake and delivery valve means adapted to thischamber, a cap member of a shape conformed' to that of said recess andsecured to a central portion of said diaphragm outside of said chamber,a magnet integral with said casing and providing a magnetic circuitincluding an airgap, a hollow nonmagnetic bobbin adapted to reciprocatethrough said air-gap and coupled to said cap, an electric coil wound onsaid bobbin to reciprocate in and through said air-gap and `means forsupplying periodical electric current to said coil.

2. A fluid pump device according to claim l, comprising resilient spidermeans extending bctween said bobbin and said casing and adapted tocenter said coil within said air-gap.

3. A iiuid pump device according to claim 1 comprising resilient spidermeans between said bobbin and said casing, adapted to center said coilwithin said air-gap and to exert a returning force on said diaphragm inoperation.

4. A fluid pump device comprising a casing; a recessed head plateforming a frustoconical'top or valve-box for said casing taperingtowards a base, a flexible diaphragm peripherally clamped to said plate,thus defining therewith a variable I volume fluid chamber, a centraloutlet passage and a circumferential set or" inlet passages beingprovided in said base, an annular intake valve member Within saidchamber adapted to seal the openings of said inlet passages thereinto, aspring in the form of a spider wedged at its corners in a circulargroove formed in said box around said base and thereby adapted to applysaid intake valve member against said inlet passages, av discharge valvemember resiliently applied over said outlet passage, driving meanssecured on said diaphragm over a central portion thereof opposite tosaid base, a magnet forming a magnetic circuit including an air-gap, acoil coupled to said driving means and adapted to reciprocate throughsaid air-gap, and means for supplying periodical electric current tosaid coil.

5. A fluid pump device according to claim 4 wherein said annular intakevalve member is provided with circular splines defining annular groovestherebetween and projections are pro' vided on said spring to engagesaid grooves, whereby a self centering effect -is obtained for saidintake valve member.

6. A reciprocable fluid pump arrangement, comprising, in combination, apump housing; inlet valve means and outlet valve means communicatingwith the interior of said pump housing; a reciprocable fluid displacingmember operatively connected to said pump housing and being adapted tocarry out intermittent suction and compression strokes sucking into saidpump housing during said suction strokes fluid through said inlet valvemeans and delivering from said pump housing during said compressionstrokes iiuid through said outletI valve means; a magnetic structureincluding a stationary' part and a movable part, said movable part beingconnected to said reciprocable fluid displacing member and beingarranged at a slight distance apart from said stationary part, one ofsaid parts including an electric coil and the other of said partsincluding a magnetic body so that supply of an alternating current tosaid coil will result in a reciprocating suction and compressionmovement of said movable part relative to said stationary part of saidmagnetic structure and in corresponding suction and compression strokes,re-

spectively, of said reciprocable fluid displacing member; means forproducing an alternating current having cycles being each composed of ashort and along cycle portion, the current continuously changing duringsaid short cycle portion from one peak value to the opposite peak value,said short cycle portion being substantially shorter than said longcycle portion; and means connecting said alternating current producingmeans to said coil so as to energize said coil for said suction movementof said movable part during each long cycle portion of said alternatingcurrent and-for said compression movement of said movable part duringeach short cycle portion of said'alternating current, thereby openingsaid inlet valve means during each of said long cycle portions andopening said outlet valve means during each of said short cycleportions.

7. A reciprocable fluid pump arrangement, comprising, in combination, apump housing; inlet valve means and outlet valve means communieatingwith the interior of said pump housing; a reciprocable fluid displacingmember operatively connected to said pump housing and being adapted tocarry out intermittent suction and compression strokes sucking into saidpump housduring said suction strokes fluid through said inlet valvemeans and delivering from said pump housing during said compressionstrokes fluid through said outlet valve means; a magnetic structureincluding a stationary part consisting of a magnetic body, and a movablepart connected to said reciprocable fluid displacing member andbeingarranged at a slight distance apart from said stationary part, anelectric coil arranged on said movable part so that supply of analternating current to said coil Will result ina reciprocating suctionand compression movement of said movable part relative to saidstationary part of said magnetic structure and in corresponding suctionand compression strokes, respectively, of said reciprocable fluiddisplacing member; means for producing an alternating cur-L rent havingcycles being each composed of a short and a long cycle portion, thecurrent continuously changing during said short cycle portion from onepeak value to the opposite peak value, said short cycle portion beingsubstantially shorter than said long cycle portion; and means connectingsaid alternating current producing means to said coil so as to energizesaidcoil for said suction movement of said movable part during each longcycle portion of said alternating current and for said compressionmovement of said movable part during each short cycle portion of saidalternating current, thereby opening said inlet valve means during eachof said long cycle portions and opening said outlet valve means duringeach of said short cycle portions.

8. In a reciprocable fluid pump, in combination, Walls forming a fluidchamber; a flexible wall element forming part of said walls of saidchamber, said flexible Wall element being reciprocablc from a firstposition into a second position and vice versa, said first and secondposi-4 tions of said flexible wall element corresponding, respectively,to the minimum and maximum volumes of said. fluid chamber; intake anddis-- charge. valves arranged in saidv Walls and opening, respectively,when a partial vacuum and a positive pressure are set up in said fluidchamber by a reciprocating movement of said ilexible wall element;driving means rigidly connected withY charge valves to closeandopen in acycle depend-- ing on the Wave form of the alternating current suppliedto said coil.

9. In a reciprocable fluid pump, in combination, Walls forming a iiuidchamber; a ilexible wall element forming part of said walls of saidchamber, said flexible wall element being reciprocable from a rstposition into a second position and vice versa, said rst and second.positions-of said flexible Wall element corresponding, respectively, tothe minimum and maximum volumes of said fluid chamber; intake anddischarge valves arranged in said Walls and opening, respectively, whena partial vacuum and a positivepressure are set up in said uid chamberby a reciprocating movement of said flexible Wall element; driving meansrigidly connected with saidflexible wall element; a magnetic circuithaving an air gap; a movable. coil arranged in said air gap of saidmag-neticcircuit and rigidly connected to said. driving means; and meansfor supplying a low frequency current tov said coil so as toreciprocatel thesamein said air gap, Whereby said flexible Wall elementis imparted a reciprocating movement` causingv saidintake and dischargevalves. to` close and open in a cycle depending on the Wave form of thelow frequency current'supplied to said coil.

l0. In a reciprocable iluid pump, in combination, walls forming a fluidchamber; a ilexible wall element forming part of said Wall-s ci saidchamber, said iiex-ible wall element being reciprocable from a iirstposition into a second position and vice versa, said first and secondpositions of said flexible Wall element corresponding, respectively, tothe minimum and` maximum volumes oi4` said fluid chamber; intake anddischarge valves arranged insaid:v Walls; and: opening, respectively,when a partial vacuum and a positive pressure are set up in said fluidchamber by'areciprocating movement oi' said flexible Wall element;driving means rigidly connected with said flexible wall element; amagnetic circuit having an air gap; a movable coil arranged in said airgap of said magnetic circuit and rigidly connected to said drivingmeans; and means for supplying a low frequency current to said coil soas to reciprocate the same in said air gap, said supplying meansincluding a Wave form distorting device, whereby said flexible wallelement is imparted a reciprocating movement causing said intake anddischarge Valves to close and open in a cycle depending on the wave formci the low frequency current supplied to said coil.

l1. In a reciprocable iiuid pump, in combination, walls forming a fluidchamber; a iiexible wall element forming part of said walls of saidchamber, said flexible Wall element being reciprocable from a firstposition into a second position and vice versa, said rst and secondpositions of said ilexible wall element corresponding,

respectively, to the-minimum and maximum vol-- umes of said fluidchamber; intake anddischarge valves arranged in said Walls and opening,respectively, when a partial vacuum and a positive pressure are set upin said fluid chamber by a reciprocating movement of said flexible wallelement; driving mea-ns rigidly connected with said.v flexible Wallelement; a magnetic circuit havingv an air gap; a movable. coil arrangedin said air gap of said magnetic circuit and rigidly connected to saiddriving means; and means for supplying a low frequency current to saidcoil so as' to reciprocate the' same in said air gap, saidl supplying'means including a rectifying device distorting the Wave form of the lowfrequencyv current, whereby said 'flexible wall element is imparted areciprocating movement causing; said intake and discharge valves toclose and open in a cycle depending on the wave form of the lowfrequency current pplied to said coil.

12. In a reciprocable iiuid pump, in combina.- ticn walls forming afluid chamber; a flexible. Wall element formingr part of said walls ofsaid chamber, said flexible Wall element being reciprocable from a nrstposition into a second position and vice versa, said first and secondpositions of said exible wall element corresponding, re.- spectively, tothe minimum and maximum volurnes of said fluid chamber; intake anddischarge valves arranged in said walls and opening,` respectively, whena partial vacuum and apositive pressure are set up in said fluid chamberby a reciprocating movement oi said flexible wall element; driving meansrigidly connected with saidv ilexifble wall element; a magnetic circuithaving an air gap; a movable coil arranged in said air ci magneticcircuit and rigidly connected to said driving means; and means for.supplying a low frequency current to said coil so as.

to reciprocate the same in said air gap, said supplying means includinga wave form distorting device, whereby said ilexible Wall element isimparted a reciprocating movement causing said intake andv discharge;valves toclo-se and open in a cycle depending ony the wave form of thelow frequency current supplied to said coil, the distorted wave form ofthe alternating current supplied to said coil consisting of ashort cyclepor;- tion and a long cycle portion being substantially longer thanvsaid short cycle portion, saidA coil being, arranged so as to causesaidA flexible Wall element to set up a positive pressure during saidshort cycle portionv and a partial vacuum during said long cycleportion.

13. In a reciprocablev fluid pump, in combination, walls forming a uidchamber; a flexible Wall element forming part of said walls of saidchamber, said ilexible wall element being reciprocable from a iirstposition into a second position and vice versa, said first and secondpositions of said exible wall. element corresponding, respectively, tothe minimum and maximum volumes of said fluid chamber; intake anddischarge valves arranged in said Walls and opening, respectively, whena partial vacuum and a positive pressure are set up in said uid chamberby a reciprocating movement of said flexible Wall element; driving meansrigidly connected with said flexible Wall element; a magnetic circuithaving an air gap; a movab e coil arranged in said air gap of saidmagnetic circuit and rigidly connected to said driving means; and meansfor supplying a low frequency current to said coil so as to reciprocatethe same in said air gap, said supplying means including a wave formdistorting device,

whereby said flexible wall element is imparted a reciprocating movementcausing said intake and discharge valves to close and open in a cycledepending on the wave form of the low frequency current supplied to saidcoil, the distorted wave form of the alternating current supplied tosaid coil consisting of a short cycle portion and a long cycle portionbeing substantially longer than said short cycle portion, said coilbeing arranged so as to cause said flexible wall element to set up apositive pressure during said short cycle portion and a partial vacuumduring said long cycle portion, said long cycle portion consisting of aiirst part having a duration approximately equal t that of said shortcycle portion and a second part during which the distorted wave formremains substantially constant.

14. In a reciprocable fluid pump, in combina tion, walls forming auid'chamber; a flexible wall element forming part of said walls of saidchamber, said flexible Wall element being reciprocable from a firstposition into a second position and vice versa, said first and secondpositions of said flexible wall element corresponding, respectively, tothe minimum and maximum volumes of said fluid chamber; intake anddischarge valves arranged in said Walls and opening, respectively, whena partial vacuum and a positive pressure are set up in said fluidchamber by a reciprocating movement of said flexible Wall element;driving means rigidly `connected with said flexible Wall element; amagnetic circuit having an air gap; a movable coil arranged in said airgap of said magnetic circuit and rigidly connected to said drivingmeans; and means for supplying a lovv frequency current to said coil soas to reciprocate the same in said air gap, said supplying meansincluding a rectifying device distorting the Wave form of the lowfrequency current, whereby said exible Wall element is imparted areciprocating movement causing said intake and discharge valves to closeand open in a cycle depending on the Wave form of the low frequencycurrent supplied to said coil, the distorted Wave form of thealternating current supplied to said coil consisting of a short cycleportion and a long cycle portion being substantially longer than saidshort cycle portion, said coil being arranged so as to cause saidilexible wall element to set up a positive pressure during said shortcycle portion and a partial vacuum during said long cycle portion.

.15. In a reciprocable fluid pump, in combination, Walls forming a iluidchamber; a flexible Wall element forming part of said Walls of said l2chamber, said flexible wall element being reciprocable from a rstposition into a second position and vice versa, said first and secondpositions of said flexible Wall element corresponding, respectively, tothe minimum and maximum volumes of said fluid chamber; intake anddischarge valves arranged in said Walls and opening, respectively, whena partial vacuum and a positive pressure are set up in said fluidchamber by a reciprocating movement of said flexible wall element;driving means rigidly connected with said flexible wall element; amagnetic circuit having an air gap; a movable coil arranged in said airgap of said magnetic -circuit and rigidly connected to said drivingmeans; and means for supplying a low frequency current to said -coil soas to reciprocate the same in said air gap, said supplying meansincluding a rectifying device distorting the Wave form of the lowfrequency current, whereby said flexible Wall element'is imparted areciprocating movement causing said intake and discharge valves to closeand open in a cycle depending on the Wave form of the low frequencycurrent supplied to said coil, the distorted Wave form of thealternating current supplied to said coil consisting of a short cycleportion and a long cycle portion being substantially longer than saidshort cycle portion, said coil being arranged so as to cause saidilexible wall element to set up a positive pressure during said shortcycle portion and a partial vacuum during said long cycle portion, saidlong cycle portion consisting of a rst part having a durationapproximately equal to that of said short cycle portion and a secondpart during which the distorted Wave form remains substantiallyconstant.

SHELLEY PRESENTEY.

vReferences Cited in the le of this patent UNITED STATES PATENTS NumberName Date 458,873 Van Depoele Sept. 1, 1891 507,946 Van Depoele Oct. 31,1893 519,652 Carpenter May 8, 1894- 520,83@ Thomson June 5, 18941,330,442 Trurnble June '7, 1921 1,713,073 Carter May 14, 1929 1,737,387Redmond Nov. 26, 1929 2,435,003 Hasselhorn June 27', 1948 2,558,329Abott June 26, 1951 FGREIGN PATENTS Number Country Date 585,298 Germany1933

